Alumasc ZinCo Intensive green roof systems offer an ecological and constructional solution to accessible and creative roof landscaping.

Intensive green roofs are similar to domestic gardens, utilising lawns, planted areas, garden furniture, water features etc, and are intended to act as accessible recreational areas. Areas of hard landscape can also be included.

A wide variety of species can be planted in an intensive green roof, giving year round colour and coverage, and total design flexibility. Intensive Green Roofs require regular irrigation and maintenance appropriate to the specified plants needs.

Alumasc ZinCo Extensive green roof systems offer an ecological and constructional solution to low-maintenance roof landscaping. Extensive green roofs require no irrigation and low maintenance, utilizing wind, frost and drought resistant self-regenerating plants such as sedums, herbs, wild grasses, mosses and heathers. These areas are not intended for access or recreation.

Areas of hard landscape can also be included. Extensive roofs are often considered where a low maintenance green roof is required purely for planning or ecological purposes.

Alumasc ZinCo Semi-intensive green roof systems offer an ecological and constructional solution to low-maintenance roof landscaping, with year-round colour, using shrubs and plants such as heathers and lavenders.

Semi-intensive green roofs require relatively little maintenance and periodic irrigation, and are not intended for access or recreation. Areas of hard landscape can also be included.

Semi-intensive roofs are often considered where a relatively maintenance-free green roof is required for planning or ecological purposes.

Biodiversity roofs (originally known as & still sometimes erroneously called “brown roofs” or “rubble roofs”) were designed originally to provide a habitat which replicated derelict, ruined or abandoned buildings (sometimes referred to as “brownfield” sites) suitable to attract the Black Redstart (a bird of the Chat and Thrush family), which once thrived on bombsites in Great Britain in the aftermath of World War II, but which became an endangered species as the sites were built upon.

Since then, biodiverse landscapes have been developed to attract a wider range of flora and fauna. A bio-diverse green roof is one which utilises a free draining substrate such as the Rockery type to support wildflowers and/or grasses which will attract a variety of wildlife.

The substrate on these roofs would ideally vary in depth to create hollows which provide cover for birds, and would be further enhanced by random placements of logs, rocks, stones and shallow pools etc which provide further cover and habitat.

These roofs can be planted with specific seed mixes to create the type of landscape required, such as meadow, wetland or woodland for example. In some cases the client may wish to allow the roof to develop it’s own vegetation by leaving the substrate unplanted so that randomly dispersed (e.g. wind-blown or bird-carried) seeds can find their way onto the roof and germinate naturally.

The rate and nature of the development of this type of roof is very difficult to predict as it is entirely dependent on chance events.

The cost of green roofs varies greatly with size, type of planting and complexity.

It should also be considered that the addition of a green roof reduces the drainage capacity requirement, extends the lifespan of the waterproofing, and improves the thermal insulation and acoustic properties of the roof, thus resulting in some reductions in building and operating costs.

Contact Alumasc for indications of installed costs for specific projects. 

Lightweight extensive green roofs can be designed to weigh as little as 65kg/m² and can even be used on lightweight decks such as profiled metal.

Intensive green roofs may utilise significant depths of soil depending upon the type of planting required.

Weights start at around 200kg/m² where low-lying plants and grasses are specified, rising to circa 300kg/m² where lawns and shrubs are required, 400kg/m² to support hedges and bushes, and up to 900kg/m² locally around trees and large bushes.

Installation window

The moisture retention layer, drainage layer and substrate can be installed all year round. However, the installation of the plant layer by the hydroplanting method is season sensitive.

The optimal planting time for hydroplanting is September to October inclusive. Also acceptable is March to April inclusive. Other times are possible although this will be dependent upon project location and environmental conditions. May to August should be avoided.

Rates of cuttings/Seeds pr m² and coverage times

We recommend a minimum cutting density of 100g of prepared and primed cuttings and seeds per m². However 200g per m² would be optimal. Coverage rates will be affected by:-

1. Season of application. Fastest coverage from autumn application.
2. Points of origin density. As important as weight per m² is how many pieces of primed material are applied per m².
3. Species selected.
4. Project location.

At 150g per m² cutting and seed material applied during the September to October period, we would expect 60% coverage by the following summer. Viewed from the ground the roof will appear to be well covered.

All plant material will be spread by hand and covered with liquid applied mulch containing paper, coir fibre, stabiliser and appropriate organic nutrient source. This method ensures minimal damage to plant material.

Extensive green roofs incorporating sedums can be planted by either plug-planting, hydroplanting, or by installing pre-cultivated sedum mats. Although hydroplanting is the most economical method, it will take two full growing cycles to achieve good coverage.

Plug-planting will give immediate coverage, but the amount of coverage depends entirely upon the frequency of planting. A good cost-effective solution is to plug-plant at 15-20 plants/m² and to infill between the plants with hydroplanting, which will eventually give complete coverage.

Sedum mats will provide immediate total cover, but need to be ordered well in advance to ensure availability. The contract also needs to be very carefully co-ordinated because the sedum mats need to be installed and watered in within a short time of delivery, as they have a limited transit life.

Intensive green roofs on the other hand, can be created in any way the client desires i.e. by seeding, or planting seedlings/saplings, semi-mature trees and shrubs, turf etc. Intensive green roofs allow total design creativity and can be used with any combination of hard landscaping, roof/garden furniture and even water features such as ponds and fountains.

Extensive green roofs require no additional irrigation after the initial watering in period, whereas intensive green roofs require irrigation in much the same way as a domestic garden does. Systems available include pop-up sprinklers and irrigation pipes, and, of course, manual watering.

Intensive green roofs require regular irrigation. The Alumasc/Zinco irrigation System employs the simple principle of an automatically topped up reservoir of water pooled beneath the drainage layer, irrigating by diffusion up through the soil, is economically and environmentally the ideal solution. Please contact our technical department for details. Other types of irrigation systems are also appropriate for use on Intensive Green Roofs.

Prior to installation of the green roof, the outlets should be plugged, and the roof temporarily flooded. Because of unavoidable differences in levels, the water will be deeper at some points than others.

The automatic irrigation units should be located where the water is deepest, and calibrated so that there is water coverage of at least a few millimetres at the shallowest points. The larger B52 units are designed for use only immediately adjacent to the outlets, whereas the smaller B32 units can be positioned anywhere on the roof, regardless of outlet positions.

Alumasc will advise on the exact number and location of units for each specific project.

Maintenance of the planted element in the two years following the installation should be included in the tender price and will consist of a minimum of two visits per year. No irrigation will be required once the plant layer is established. Procedures carried out in the first twelve months could include the following:-

1. Removal of unwanted plant material.
2. Application of nutrient source.
3. Removal of dead flower heads (if required).
4. Checks on outlets and drainage.
5. Replenishment of any areas of settled substrate.
6. Correction of any localised plant system problems.
7. Replacement of any failed plants exceeding 5% of total plants installed.

Points 5, 6 and 7 are generally confined to year one. Subsequent years will see maintenance requirements reduce as the plant system establishes. At the end of the two year post installation maintenance, we would recommend that the client considers negotiating a continuing programme of maintenance with the contractor on the basis that they will be familiar with what is required to maintain a healthy plant regime.

Intensive green roofs will require similar maintenance to any normal recreational/decorative garden, i.e mowing of grass, weeding, pruning, removal of dead vegetation etc. Aeration of the specialist ZinCo soil would not be required as it is non-compacting and porous.

Due to settlement after installation, it is necessary to multiply the calculated volume of soil required by a settlement factor:

Roof Garden Substrate: Multiply by 1.30 or add 30%
Heather with Lavender Substrate: Multiply by 1.25 or add 25%
Rockery Type Plant Substrate: Multiply by 1.20 or add 20%
Cranberry Bog Substrate: Multiply by 1.30 or add 30%
Sedum Carpet Substrate: Multiply by 1.12 or add 12%
ZinColit crushed brick infill: Multiply by 1.08 or add 8%

E.g: for 100m² of 70mm sedum carpet substrate you would require 100m2 x 70mm + 12%. So the calculation is 100 x 0.07 x 1.12 = 7.84m³.

Contact the Alumasc technical department for confirmation of volume required if necessary.

No – because ordinary soil would quickly become clogged and waterlogged, only specialist green roof soil can be used in a green roof system.

These specialist soils are non-compacting, non-clogging, weed and stone free, fire retardant and almost half the weight of standard topsoil.

Alumasc ZinCo green roofs can be installed up to 30°, (steeper in some cases) using a combination of special drainage layers and anti-erosion matting. Alumasc Technical Services must be contacted for advice in such cases.

Extensive green roofs require no additional irrigation after the initial watering in period, whereas intensive green roofs require irrigation in much the same way as a domestic garden does.

Systems available include pop-up sprinklers and irrigation pipes, and, of course, manual watering.

Intensive green roofs require regular irrigation. The Alumasc/Zinco irrigation System employs the simple principle of an automatically topped up reservoir of water pooled beneath the drainage layer, irrigating by diffusion up through the soil, is economically and environmentally the ideal solution.

Please contact our technical department for details. Other types of irrigation systems are also appropriate for use on Intensive Green Roofs.

The rainwater from a green roof is classified as surface water. 

Green roofs absorb a significant amount of rainwater.

Depending upon the depth of soil, up to 70% of rainwater may be retained and eventually evaporate, with only 30% actually discharging via the rainwater disposal system. Alumasc Technical Services can calculate the required rainwater disposal capacity in order to optimise the design of the drainage system.

Rainwater can also be collected in a cistern to provide a source of water for irrigation purposes during dry spells, operated by a solar powered pump.